If you travel, a little or a lot, chances are you have had some issues packing the right amount for your trip. My problem is that I usually pack too much on International trips. But since most of my "extras" are disposable, I donate them to needy people, particular in Third World countries. For long weekend trips, or trips of about 5-7 days, I am the "master". Anything longer, and I bring too much!
There are some obvious rules or guidelines to follow, to pack optimally, and still enjoy your trip. I also believe that packing lighter is good, and that you can buy whatever you forgot.
The hotel will have what you need?
Generally this is true. But once in a while, they don't have a hair dryer or little shampoo bottles. Hair dryers are bulky, so a simple call to the hotel(s) will solve this problem. And for shampoo, why don't you just take one from your previous visit to a big hotel? My personal favorite is shower soap, so I always bring my own. I hate those little bars that chain hotels provide. And they do have some sundries, usually complimentary, things like shaving cream, razors, toothpaste, and nail files. The nicer hotels have great sewing kits that include scissors. Make sure you take it with you!
Read the airline's baggage policy.
I never have an issue traveling domestically. But I always know the limit of international flights. And so should you. The weight limits always catch somebody. They are the ones trying to repack their bags near the front of the line. Silly, waste of time, embarrassing, all of the above! 
Checking your bag late.
This almost always means a lost or delayed bag. If you must check a bag, do it an hour before your flight leaves. No exceptions! And tie a bright ribbon or yarn to your bag handle to make it easily identifiable.
Focus on size, not weight.
I beg to differ, weight is the key. I would rather play with a few golf clubs short than run the risk of damage or baggage fees for overweight bags. The same applies to my regular duffle bag (on wheels). If I have to haul it, pull it, lift it, or check it, then it must be manageable. Rotator cuff surgery is a bitch, I hear.
Slipping it by the TSA.
Not bloody likely. It is not worth it. They miss a few, they catch a few. Coming back form Montana last year, TSA thought I had gun powder on my hands! I do not own a gun, did not shoot one on this trip, and have no earthly idea how this happened. But I must have touched something, perhaps the handles on my rental mountain bike, a door knob, or the keys to my rental car. What a pain in the ass. They checked everything in my bag, including dirty laundry, toiletries, and souvenirs. Furthermore, I do not trust them with anything valuable. Leave the valuables at home!
Not making a packing list
The list should be a ritual, unless you have a photographic memory. I once forgot my golf clubs on a two week trip to Hawaii. And I have forgotten toiletries once as well. But I learned my lesson, have not done it again, and use a list, particularly for longer trips.
Getting rid of your packing list
Would you believe it comes in handy when packing and repacking on a long trip? How many times have you forgotten something, like a night light, toiletry, or jacket in the closet? At least keep a list of valuables! Better yet, just leave everything in the suitcase or bag until your next trip.
Special care for liquids
I always keep liquids in a plastic bag, usually a baggie. Many times the altitude on the plane will force open a container of sunscreen or moisturizer. I generally do not carry alcohol (wine or champagne) in my bag. But if I do, I use a waterproof container, and lots of padding. When my kids were young, the disposable diaper was great padding for wine bottles.
Sneaking an oversize bag onto the plane
I hate those who do it! Some people are always pushing the envelope. Then there is the guy who has his roller bag, and a duffel bag large enough for the entire basketball team! I believe this is one rule that should be enforced. After 2 violations, a fine should be levied.
Please wear socks
Is there anything more gross that someone with resting their bare feet on your stuff? Or resting their feet on your arm rest? Do you think they have any chance of surviving a fire on the plane in flip flops?
Want me to keep going?
Fold or roll your clothes
Whichever one you do, both work. Use the method you are most comfortable with.
Leave room for purchases
I always leave room for a purchase. You should too!
Always carry bedroom slippers or sandals
I cannot imagine anything dirtier or more unpredictable than a hotel floor. Or worse yet, a bath tub or shower stall. Protect your feet from athlete's foot, needles, dirt, and even foxtails and stickers. I like the little throw away ones the airlines give in business and first class.
Always carry extra ziplock bags
These come in handy for liquids, dirty laundry, wet clothes, purchases, and small items like jewelry, cuff links, coins, and phone chargers. Be prepared! If you were in the Scouts, you know this one. Always have a band aid, pain reliever, handkerchief or Kleenex, handy. Duck tape and some light rope are always handy. The duck tape to cover a loudmouth's mouth, and light rope to tie them to a moving train. Buy or rent at your destination Bulky items, or throw aways should be purchased at your destination. These items include sunscreen, beach towels, large hats, plastic champagne glasses (my personal favorite), swim suits, gym clothes, bedroom slippers, and umbrellas. And I can always rent golf clubs, surf boards, and bicycles at my destination. I am open to any suggestions you might have. The best one wins a prize! (Sally won!)
